This cooperative study of these common congenital heart defects (ventricular septal defect, aortic valve stenosis and pulmonary valve stenosis) has three major overall objectives: 1. The study of the natural history of patients with such defects and to assess the effects of medical and surgical treatment upon this natural history. Information will be provided to help predict the clinical course in an individual patient from age, clinical symptoms and signs, electrocardiographic, vectorcardiographic and x-ray findings and cardiac catheterization data. 2. To provide a basis for more knowledgeable decisions regarding advisability of surgery in patients in whom the comparative merits of medical and surgical treatment are currently in doubt. 3. To correlate hemodynamic measurements in individual patients with the clinical examination, electrocardiogram and vectorcardiogram, chest x-ray and to improve the ability of the clinician to evaluate hemodynamic abnormalities indirectly without cardiac catheterization.